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Without having known about your post, I wondered on the same thing a few months later.
I wanted an image that runs as a perl script without the -x switch or any other switches.
First, I've decided that this was impossible to do with a PNG image, because perl chokes right away on its header.
Then, I was looking at GIF, but I've found the specs too complicated, so I took it away.
I've however produced a BMP (windows bitmap) that doubles as a JAPH. BMP is now displayed in most browsers, however it's not allowed to upload one as a monk image (maybe because when this was decided, Netscape 4 which doesn't have BMP support, was still common back then). Thus, I can only show this image off-site: japh.bmp.
To try the perl part, download it and run with perl japh.bmp.
(The japh this one has is a trivial one, but I can change it to any perl code of course.)